Over the past five years, thanks to support from NICHD, we have been actively studying the time-course and neural correlates of word processing in university students learning a second language. In this work we use the event-related potential (ERP) technique, which provides a noninvasive and cost effective online measure of neural activity that can be used to study the underlying organization and processing of words in both of a bilingual's two languages. Our studies have provided important insights into the neural, perceptual and cognitive mechanisms involved in acquiring a vocabulary in a new second language (L2), as well as showing how such learning impacts native language (L1) processing. This work has led us to describe a new developmental interactive-activation model of second language acquisition which will be tested in three sets of interrelated studies in the research outlined in this proposal. To date our studies have focused on complementary populations of French and English university learners of a L2. In this competing renewal our first aim is to follow-up on the results of studies using several of our most promising ERP paradigms in two groups of more proficient balanced bilinguals: one that learned both of their languages early in life;and a second that learned one language early and the other after age 10. In a second aim we propose to continue our study of French/English university learners, but to also expand our ERP studies to L1 English and French learners of two non- Indo-European languages that either use a completely different writing system than western languages (Japanese) or use a similar writing system, but a different alphabet (Arabic). Finally, our third aim is to extend our ERP studies to learners who are at the very beginning of acquiring a visual vocabulary in a new L2. In these studies learning will take place under controlled laboratory conditions and the progression of learning over a period of nine training sessions will be tracked. Changes in both ERP measures and language competence on items in the new L2 vocabulary will be monitored. Together these studies will help us fill important gaps in knowledge about the neural organization and interrelationship of word processing in second language learners. PUBLIC HEALTH RELEVANCE: In most of the world bilingualism is the norm. Even in the primarily monolingual US, there is a growing awareness that knowledge of a second language (L2) is essential to our competitiveness. However, there are critical gaps in our understanding of how L2s are learned and processed as well as how learning a second language influences native language processing. The proposed studies will provide critical information about the mental and neural underpinnings of L2 acquisition.